The phenomenon of mRNA trans-ligation is a poorly understood process in need of novel experimental techniques and insight. This proposal will study mRNA trans-ligation in human cancer cells that was discovered as a response to treatment with a clinically relevant ribonuclease. The extent of mRNA trans- ligation induced by ribonucleases will be characterized by RNA sequencing techniques. An enzyme hypothesized to be responsible for the observed mRNA ligation will be characterized kinetically and mechanistically. A combination of cellular studies and in vitro characterizations of mRNA ligation will bring to light important details about this uncharacterized physiological process. A fundamental understanding of mRNA trans-ligation is likely to lead to an understanding of various normal physiological and disease processes.